Electrical conductor



Aug. 21, 192s. 1,681,541

J.- JQHNSTON ELECTRICAL CONDUCTOR Filed May 5, 1924 /fl//e/f/a/- Jah/7 Jah/752W? CII Patented Aug. 2l, 1928.

. UNITED STATES 1,681,541 PATENT OFFICE.

JOHN JOHNSTON, OF NEW HAVEN, CONNECTICUT, ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, 0F NEW YORK, N; Y., A CORPORATION OF NEW YORK.

ELECTRICAL CONDUCTOR.

Application filed May 5,

lated electrica-l conductors of submarinel cables.

It is an object of the invention to improve the insulation of such conductors both electrically and mechanically and to apply the insulating material to the conductor 1n such a manner as not toaffect deleteriously the conductor itself and in the case of a loaded conductor to apply the insulating material in such a manner that the loading material With which the conductor 1s Wrapped Will not be subjected to strains.

The use of hard rubber or semi-hard rub-v ber as the material for insulating submarine conductors oii'ers important advantages because of its low conductancetloyv dielectric constant, and the fact that it is more rigid than soft rubber and its swelling by absorption of water is very limited. rlhese advantages of hard rubber insulation for submarine cables are pointed out more in detail in a copending application of Williams 'et al., Serial No. 678,509 filed Dec. 4, 1923. On the other hand, it is very difficult if the rubber compound is vulcanized on the conductor to maintain an even thickness of insulation about the conductor during the long vulcanizing process 'necessary and, furthermore, the action of the sulphur on the conductor is objectionable because of its progress during the long period of heating. Moreover, vulca-nization of the rubber compound on the conductor cannot be accomplished satisfactorily in the case of a continuously loaded conductor of an improved type recently developed. In this conductor, a recently discovered alloy is employed for the loading material, such alloy having a permeability at loW magnetizing forces far in excess of that obtained with the best grades of iron Wire employed heretofore for Icontinuous loading. For a more complete description of this alloy and its characteristics reference is made to U. S. Patents No. 1,586,884, June 1, 1926, to G. W. Elmen, and No. 1,586,874, June 1, 1926, to O. E. Bucklev. However, to obtain the best results with this new alloy when used in submarine cables it is necessary to protect it from mechanical strains induced by hydrostatic pressure exerted on it when laid on the ocean floor and to protect against such strains, it has been found desirable to im- 1924. Serial No. 711,039.

pregnate the loaded conductor `With an insulating compound such as liquid bitumen that fills all the interstices between adjacent turns of the loading material and between ,the loading material and the conductor, and,

in the case of a stranded conductor between individual strands of the conductor itself. To this end, it is preferable to employ an iinpregnating material which Will flow at the temperatures and pressures encountered in great depths of Water as disclosed in a copending application of Archie R. Kemp Serial No. 617,511, filed Feb. 7, 1923. It is not satisfactory to vulcanize the rubber compound on a core of this type of conductor in which a\ layer of liquid bitumen is provided under the insulating material, since the liquid bitumen mixes with the rubber compound during vulcanization and hardens to such an extent as to render it useless in protecting the loading material from subsequent strains.

To provide an insulated conductor having the desired characteristics, the invention contemplates the use of an insulating tape consisting of hard rubber or semi-hard rubber which is lirst vulcanized and then rendered suliciently plastic to permit it being formed to fit'the conductor and the` seams jointed by means of heat and pressure.

In the accompanyingdrawing, Fig. 1 is a view partly in section, of apparatus for heating and Wrapping the tape about the conductor and then joining the seams by passing through a suitable rolling mechanism; Fig. 2 is a sectional view taken along the' line 2-2 of Fig. 1;'Fig. 3 is a sectional view taken along the line 3-3 of Fig. 1, showing the construction of a die or forming the insulating tape into a sui/ able tube surrounding the conductor; Fig. 4 is a sectional end view along the line 4 4 of Figure 1 of the rolling mechanism and Fig. 5 is a sectional View along line 5-5.of Figure 1 of a conductor insulated in accordance With this invention.

Referring to the drawing, the conductor 6 and insulating tape 7 are passed at a predetermined speed through an oven 8 which is maintained at a constant temperature of approXimately 150o C. by means of a gas heater 9 or other suitable means. As the conductor and tape pass through the die 10 the tape which is softened .by the temperature of the oven is progressively fashioned than the diameter of the conductor as it emerges from the die 10. The lower edges of the rollers are preferably shaped as shown at 13 so that any excess insulatingpmaterial is sheared ofi. lWhile the rollers, as shown, are mounted av short distance from the oven, it is obvious that in jiractice-the57 Will be mounted sufficiently close so that there Will be no chance for cooling of the rubber compound before it passes between the rollers.

In order that the tape may be more-easily rendered plastic as it passes through the oven, it is desirable to include in the rubber compound a thermo-plastic material such as bitumen, preferably one of the harder varieties. lWhile the condition of the insulating compound will obviously depend upon the temperatures employed in the oven and the pressures maintained by the rollers, a compound Which may be used at temperatures of 150O C. or somewhat less, Consists ofap proXimately 60% rubber, 20% sulphur and '20% bitumen.' rlhis compound is vulcanized at temperatures corresponding to from. 90 to 100 pounds steam pressure until the free sulphurl content is reduced to .5% or less, in a manner such as is nov commonly employed in the rubber industry. lin place, of, or, in addition to, adding a bitumen to render the vulcanized compound more thermoplastic, it is possible to use in Whole or in part the material made in accordance with the process described in a copending application of Archie R. Kemp, which has issued as Patent 1,638,535 on August 9, 1927. This material in its preferred composition is composed or raw rubber compounded With 15% of sulphur by Weight and it is thoroughly mixed by Working in a standard rubber mill. The term hard rubber7 as used in the specification and claims is intended to include also what is sometimes referred to as. semihard rubber in which the sulphur content may be as loW as 15%.

lVhat is claimed is:

1. The method of insulating a conductor Which consists in vulcanizing `insulating materia-l, forming a tape of said insulating maductor, and joii Leanser terial, applying said tape to closely surround said conductor, and joining the edges of said tape to provide a continuous sheath of insulating material.

2. The method of insulating a conductor which consists in vulcanizing rubber, forming a tape of said vulcanized rubber, applying said tape to closely surround the conthe edges of said tape mus sheath of insulating to provide a con material. l

3. The method insulating a conductor which consists in vulcanizing insulating material, forming a tape, heating the vulcanized tape, forming it While hot about the conductor, and joining the edges of the hot tape by the application of pressure to provide a continuous sheath of insulating material.

11. lThe method of insulating a conductor with insulating material which consists in compounding rubber, sulphur and bitumen, vulcanizing said compound until the free sulphur content is reduced to .5% or less, heating the vulcanized material, forming it While hot about the conductor, andsubjecting it to pressure to provide a continuous sheath of insulating material.

5. The method of forming a continuous sheath of vulcanized hard rubber about a conductor, which method consists in vulcanizing rubber, rendering plastic said rubber by adding bitumen, heating saidconductor and a tape of said vulcanized rubber to a temperature of approximately 150O C., formingl the tape about the conductor while heated, Aand immediately thereafter applying to the conductor With the tape formed thereabout sufficient pressure to join the edges of the tape and press it into the desired shape.

6. The method vof insulating a 'composite conducting core impregnated With fluid pressure equalizing means, Which consists in forming a tape of vulcanized insulating materialto closely surround said core, said `fluid pressure equalizing means being incapable When in contact With said-insulating material of withstanding the temperatures required for -vuleanizing said material for a suicient time to permitl vulcanization of the -tape in situ onA said core, and joining the edges of said tape by the application of pressure to provide a Continous seamless sheath of 'insulating material.

In Witness'whereof, I hereunto subscribe my name this 2 day of May, A. D., 1924.

JonN Joi-iusrou.V l 

